This invention relates to immersion heaters and more particularly, to electrical immersion heaters for use in chemically corrosive environments and a method for manufacturing such heaters.
In certain manufacturing processes, it is necessary to heat a vat or tank of chemicals. One way this is done is to immerse an over-the-side electrical heater in the chemical, and circulate an electrical current through the heater's heating element. In many instances, the chemicals being heated are corrosive and as such, attack the heater. Consequently, heaters of this type have a sheath of protective material over their heating element and, in addition, some type of coating is applied over the sheath. Until now, there has been a persistent problem in finding an adequate coating which can withstand the rigors of both the environment in which immersion heaters are used and the operation of the heater, especially at higher watt-densities. One problem encountered with previous coatings, for example, is their tendency to have or form pin holes. This, of course, allows the chemicals to penetrate the coating and attack the sheath and ultimately the heating element. The result is either a failure of the heater or its early replacement. Another problem with previous coating materials is their tendency to separate from the sheath when the current flow through the heater produces high watt-densities. This again ultimately allows the chemical environment to attack the heater and cause it to fail or need to be replaced.
Among the several objects of the present invention is to provide a metal sheathed immersion electrical heater for use in a chemically corrosive environment with a coating that is less liable to have or form pinholes than such heaters known heretofore.
Another object is to provide such a heater with a coating capable of withstanding both prolonged exposure to the environment and the operation of the heater at high watt-density levels without losing its coating properties.
Still another object is to provide a method for manufacturing an immersion heater with the protective coating.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.